Chromatography is a preferred method for the analysis of samples. In particular, gas chromatography is particularly good for environmental samples as impurities and contaminates in most environmental are not complex molecules. More complex molecules necessitate the use of supercritical fluid chromatography or liquid chromatography. Prior to the introduction of a sample into a chromatographic instrument, the sample must be prepared such that components of interest can be extracted from the sample.
Solid phase extraction (SPE) is a technique which utilizes a flow-through chamber that contains a large number of small inert silica particles each coated with a stationary phase material. The liquid sample is flushed through the cartridge and the components of interest diffuse into the stationary phase coating. A solvent having a high solubility factor for the components of interest is then flushed through the cartridge, thereby dissolving and carrying away the components of interest for analysis. The Hewlett-Packard 7686 PrepStation System is an example of a system that provides for fully automated SPE, including filtering, heating and evaporating. After sample preparation is complete, components of interest are typically dissolved into a solvent and temporarily stored in a sample vial. A syringe is typically employed for aspirating the solvent containing components of interest and injecting them into an appropriate chromatographic apparatus. The syringe may be operated manually or automatically using automatic injection apparatus. See, for example, U.S. Pat. No. 4,615,226 entitled "Apparatus and Method for Introducing Solutes into a Stream of Carrier Gas of a Gas Chromatograph" issued on Oct. 7, 1986 to DiNuzzo et al.
A technique for carrying out Solid Phase Microextraction (SPME) without the use of solvent is disclosed in International Application Number PCT/CA91/00108 entitled "Method and Device for Solid Phase Microextraction and Desorption" by Janusz B. Pawliszyn. A solid fused silica fiber coated with a secondary phase is attached to the plunger mechanism of a standard syringe such that the fiber can be extended from inside the hollow syringe needle. The needle is inserted through a septum and into a vial. The plunger is depressed so that the fiber will extend into the sample such that the components of interest diffuse into the stationary phase coating until equilibrium is reached, whereupon, the fiber is withdrawn into the needle and the needle is withdrawn from the sample vial. Continuous mixing of the sample during the diffusion step shortens the period required for equilibrium. The needle is then inserted through a septum and into injection port of a gas chromatograph such that the components of interest are then thermally desorbed and cryofocused on the column.
The quantity of components of interest that are absorbed is directly related to the surface area and thickness of the stationary phase. Increasing film thickness to increase capacity has the detrimental effect of slowing the rate of absorption. Thus, a problem with SPME is its limited flexibility regarding film thickness. SPME is problematic due to the inherent fragility of fused silica when extended through a syringe needle, and because the stationary phase coating on the outer surface of the fused silica is unprotected when extended.
There is a need for a robust sample preparation technique which reduces or eliminates the amount of solvent required for sample preparation.